The present invention relates to an intracranial pressure relief valve and, more particularly, to a three stage CSF pressure relief valve having an adjustable valve closure member which establishes valve opening pressure, and an adjustable valve stem member of improved construction which establishes the pressure levels at which the valve transitions from a first constant pressure mode to a constant flow mode, an from the constant flow mode to a second constant pressure mode.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles of the brain. The excessive collection of CSF in the ventricles results in an abnormal increase in epidural and intradural pressures, which may cause a number of adverse physiological effects including compression of the brain tissue, impairment of blood flow in the brain tissue, and impairment of the brain's normal metabolism.
Treatment of a hydrocephalic condition frequently involves relieving the abnormally high intracranial pressure. To this end, a variety of CSF pressure relief valves and methods of controlling CSF pressure have been developed which include various check valves, servo valves, or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to a suitable drainage location in the body, such as the venous system or the peritoneal cavity, and, in their simplest form, operate by opening when the difference between CSF pressure and pressure in the discharge line exceeds a predetermined level.
The use of a simple check valve in the treatment of hydrocephalus is potentially disadvantageous since it is possible for such a valve to open in response to a sudden, but nevertheless perfectly normal, increases in differential pressure between CSF in the ventricular spaces and fluid at the drainage location, resulting in abnormal and potentially dangerous hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, the resulting increased vertical height of the fluid column existing between the head and the drainage location may result in such an increase in differential pressure. Accordingly, three stage CSF pressure relief valves, such as that described in the copending application of Christian Sainte-Rose and Michael D. Hooven, enitled "Three Stage Valve", Ser. No. 672,868, filed Nov. 19, 1984, now abandoned, have been developed which serve to prevent undesired hyperdrainage by limiting the flow rate of fluid through the valve when a sudden increase in differential pressure occurs.
In a valve of preferred construction incorporating the present invention a diaphragm is movable in response to the pressure differential between ventricular CSF pressure in an inlet chamber on one side of the diaphragm, and the pressure of fluid at the drainage location in an outlet chamber on the other side of the diaphragm. The diaphragm includes a valve seat which is mounted concentrically thereon and which includes a fluid metering orifice. The diaphragm is arranged to engage an adjustable valve closure member in the inlet chamber so as to close the valve when the pressure differential falls below a predetermined minimum level. A valve stem of generally cylindrical form having a fluid metering notch on the exterior surface thereof extends through the orifice to provide in cooperation with the orifice fluid metering between the two chambers.
The motion of the diaphragm in response to changes in differential pressure between the two valve chambers causes the valve to progress through four valving conditions. In the first valving condition, the diaphragm engages the valve closure member to prevent fluid flow through the valve. In the second valving condition, when the pressure differential between the two chambers exceeds a minimum threshold level, fluid flow between the chambers is regulated by coaction between the valve seat and the valve stem to maintain a first predetermined pressure level in the inlet chamber. In the third valving condition, which occurs in response to a sudden further increase in differential pressure beyond a further threshold level, such as might be caused by a drastic change in the position of the patient, such as movement from a recumbent position to a vertical position, the valve seat and valve stem coact to maintain a substantially constant flow rate. In the fourth valving condition, where the pressure differential increases still further and exceeds a maximum threshold level, the valve seat and valve stem coact to maintain a second predetermined pressure level in the first chamber to prevent hyperdrainage.
A CSF pressure relief valve is typically miniaturized for implantation and is required to perform with a high degree of precision under highly demanding conditions throughout a rather extensive, ever-changing mode of operation. Consequently, it has been necessary to carefully control the dimensions of the various parts of the valve, particularly the valve seat, the valve stem and the orifice defined by the valve seat. The parts involved are quite small, and working tolerances on the order of 0.0001 of an inch must be met. Considerable difficulty may be incurred in manufacturing such a valve, and it is to the reduction of this manufacturing difficulty that the construction of the present invention is directed.
A CSF pressure relief valve incorporating a one piece valve stem is described in U.S. Pat. No. 4,627,832 entitled "Three Stage Intracranial Pressure Relief Valve Having Single Piece Valve Stem", which issued to Michael D. Hooven et al. on Dec. 9, 1986. Alternative constructions for the valve members are described in the copending application of Michael D. Hooven, entitled "Three Stage Intracranial Pressure Control Valve", Ser. No. 812,779, filed Dec. 23, 1985, now U.S. Pat. No. 4,714,459 issued Dec. 22, 1987, and in the copending application of Demetrios Doumenis, entitled Three Stage Implantable Pressure Relief Valve with Adjustable Valve Stem Member", Ser. No. 812,780, filed Dec. 23, 1985, now U.S. Pat. No. 4,729,672, issued Mar. 8, 1988.
The present invention is directed to an improvement in multi-stage CSF valve construction, and particularly in the valve stem of such a valve. Basically, this improvement utilizes an improved cylindrical construction for the valve stem wherein flow variations are achieved upon movement of the valve seat by the provision of a flow metering notch in the side wall of the valve stem, which allows the valve stem to be readily formed with great precision by conventional manufacturing techniques.
In view of the foregoing, it is a general object of the present invention to provide a new and improved valve for relieving intracranial pressure caused by the presence of excess CSF in the ventricles of the brain.
It is a more specific object of the present invention to provide a CSF pressure relief valve which can be more easily and economically manufactured.
It is a still more specific object of the present invention to provide a CSF pressure relief valve utilizing a one-piece valve stem of improved construction which may be more easily manufactured with high precision using conventional manufacturing techniques.